Chemical comminution of coal and removal of ash including sulfur in inorganic form therefrom

ABSTRACT

Treatment of coal with ammonia which contains water, whether the coal is in a sub-surface stratum or in large lumps as mined by standard means weakens interlayer forces at natural interfaces present in the coal. The extent to which the interlayer forces may be reduced by this treatment is such that the coal may be reduced to fragments without application of mechanical force. Further, inorganic compounds present in the coal are unaffected by said treatment, as a result of which inorganic components, and, particularly, sulfur compounds may readily be separated from the coal fragments by known means.

United States Patent [1 1 Aldrich [111 3,870,237 Mar. 11,1975

[ CHEMICAL COMMINUTION OF COAL AND REMOVAL OF ASH INCLUDING SULFUR ININORGANIC FORM THEREFROM [75] Inventor: Robert G. Aldrich, Manilius, NY.

[73] Assignee: Syracuse University Research Corp.,

Syracuse, NY.

[22] Filed: Feb. 14, 1974 [21] Appl. No.: 442,559

[52] U.S. Cl. 241/1 [51] Int. Cl. B02c 19/00 [58] Field of Search 241/1[56] References Cited UNITED STATES PATENTS 3,815,826 6/1974 Aldrich etal 241/1 OTHER PU BLICATIONS Dryden, l. G. C., Solvent Power for Coalsat Room Temperature," Chemistry and Industry, June 7, 1952, pp. 502-508.

Lazarou & Angelova, Treatment of Coal with Sodium in Liquid AmmoniaSolution," Fuel, Vol. XLVll, No. 5, Sept, 1968, PP- 333-341.

Primary ExaminerGranville Y. Custer, Jr. Attorney, Agent, or FirmBlumMoscovitz Friedman & Kaplan ABSTRACT Treatment of coal with ammoniawhich contains water, whether the coal is in a sub-surface stratum or inlarge lumps as mined by standard means weakens interlayer forces atnatural interfaces present in the coal. The extent to which theinterlayer forces may be reduced by this treatment is such that the coalmay be reduced to fragments without application of mechanical force.Further, inorganic compounds present in the coal are unaffected by saidtreatment, as a result of I which inorganic components, and,particularly, sulfur compounds may readily be separated from the coalfragments by known means.

2 Claims, 5 Drawing Figures Mu/sr lNERT Mmm/v/A F [Z 1 m COALPATENTEDHARHIQYS FIG.

COAL

STORAGE 55mm 70A CHEMICAL COMMINUTION OF COAL AND REMOVAL OF ASHINCLUDING SULFUR IN INORGANIC FORM THEREFROM BACKGROUND OF THE INVENTIONAccording to usual coal-mining procedures, subsurface coal is brokeninto pieces of manageable size by the use of explosives, picks or othermechanical means, and finally brought to the surface mostly in the formof large lumps which are then broken down by mechanical procedures suchas crushing, milling, grinding, pulverizing, etc. The degree ofreduction in size is suited to the application for which the coal is tobe used.

Methods have been disclosed wherein the addition of inorganic or organicsalts and weak aqueous solutions have supressed the formations offragments in the airborne size range during conventional coal cutting,although no particular advantage was cited in the size reductionprocesses. (Poelnev. A.P., et al., Control of Coal Dust in Mines, Akad.Nauk SSSR Sb. Statu 7 (1967), 72.).

The usual methods for the breakage of coal which is found in the naturalstate as massive solid beds include the use of drilling, cutting orexplosive mining techniques as aforenoted. All of these are normallyused in conjunction with each other and require an excessive energyexpenditure including man power. Since numerous industrial processeswhich consume coal use the extracted product inparticulate form, e.g. kinch size or less, further size reduction operations are required. Eachof these subsequent processes employed for further particle sizereduction requires large additional expenditures of energy and producesexcessive volumes of coal dust, hazardous due to its explosive natureand the effect on the health of workers carrying out the operations.

SUMMARY OF THE INVENTION The treatment of coal with moist ammoriia wherethe water content may be as high as about 70 percent of the total,results in weakening of the interlayer forces at natural interfacespresent in the coal. The weakening of the interlayer forces may sufficeto cause fracture of the coal without application of mechanical stress.The weakening of the forces is sufficiently great so that in some casesthe coal breaks into particles small enough to be carried by inert fluidor gas without application of further force. Since inorganic materials,and, in particular, inorganic sulfur compounds are unaffected bytreatment with moist ammonia, inorganic sulfurcontaining compounds aswell as other types of ash may be separated from fragmented coal on thebasis of size or density. A liquid having a density near 1.60 gm/ml isconvenient for carrying out such a separation.

The chemical comminution of coal by means of moist ammonia can be usedfor mining coal from sub-surface strata by injecting said moist ammoniainto a subsurface stratum, following this with the injection of an inertfluid at a rate high enough to form a suspension, and carrying thesuspension back to the surface where the comminuted coal is separatedfrom the carrier. A particularly valuable feature of the presentinvention is the fact that about 90 percent of the comminuted product isplus 32 mesh. Moreover, although there is some increase in the minus 100mesh quantity, most of this fraction is not so small as to be difficultto separate same from a carrier stream. Consequently, protection againstdischarge of fines into the atmosphere during processing does notconstitute a serious problem. Also, since the inorganic components ofthe coal are unaffected, most of the impurities of this type can beremoved by sieving as well as by flotation.

Since moist ammonia is effective for weakening the interfacial bonds incoal and for fragmentation of certain types of coal, the presence offree water in the coal has little effect on the process other than todecrease the rate of said process.

The process is suitable for deep-mining, strip-mining and auger-miningin that the coal after being comminuted by moist ammonia, with orwithout the use of mechanical aids, can then be carried to the surfaceor exterior with an inert gas or liquid. A suitable inert gas isnitrogen and a suitable inert liquid is water.

Accordingly, an object of the present invention is to provide a chemicalmethod for the fragmentation of raw coal. I

Another object of this invention is to provide a chemical method for thefragmentation of raw coal in natural beds, seams or sub-surface strata.

A further object of the present invention is to provide a chemicalmethod for the fragmentation of coal either as a step in mining saidcoal or subsequent to mining of said coal, thereby greatly reducing theenergy requirement for mining coal and for fragmenting same.

Another object of the present invention is to provide a chemical methodfor the fragmentation of coal which produces relatively little finesdifficult to separate from air.

An important object of the present invention is to provide a means forparticle size reduction of coal without affecting the particle size ofrock'or mineral impurities.

A significant object of the present invention is to provide a chemicalmeans for fragmentation of coal without detriment to the calorific valueof the coal.

A further object of the present invention is to facilitate theseparation of inorganic impurities and,- in particular, the separationof inorganic sulfur compounds from coal. i

Still another object of the present invention is to provide aneconomical method of mining coal in which'the expenditure of mechanicalenergy is greatly reduced.

Yet a further object of the present invention is the size-reduction ofcoal without concommitant reduction of size of inorganic components,thereby making it possible to remove said inorganic components from saidcoal by sieving.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others thereof,which will be exemplified in the method hereinafter disclosed, and thescope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of theinvention, reference is had to the following description taken inconnection with the accompanying drawings, in which:

FIG. 1 shows schematically the fragmentation and mining of coal inaccordance with the method of the present invention;

FIGS. 2, 3, 4 and 5 show the change in size distribution of twodifferent types of coal after treatment with moist ammonia and the sizedistribution for that portion of the coal having a density less than1.62.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Ammonia containing moisture ina quantity up to about 7 parts of water to 3 parts of ammonia, whenbrought in contact with massive coal, quickly impregnates the coalstructure, causing a reduction in internal boundary strength. For manytypes of coal reduction in internal boundary strength is so great thatthe massive coal system after impregnation has almost no resistance to acrushing force; some coals virtually collapse under their own weight toa finely divided product when so treated. The following is a descriptionof tests carried out on two types of coal and the results achieved. Thetwo coals were Pittsburgh Seam, District 3, Marion County, W. Va. andIllinois Number 6 Seam, District 10, Montgomery County, 111. Both coalshad previously been crushed to 1% inches top size. These coals are ofparticular interest because they present notoriously difficult problemsin the coal cleaning field and are representative of the major coals inthe Interior Basin and Appalachian Region. The Pittsburgh Seam coal hasthe following delivered nominal quality:

3.21 moisture 6.94 ash 2.51 sulfur 13,612 BTU.

The Illinois No. 6 seam coal has the following delivered nominalquality:

14.8 moisture 22.0 ash 3.7 sulfur 9,500 BTU.

One pound representative samples of the coals were placed in each of tworesin kettles and liquid ammonia was introduced into the kettles. Thequantity of liquid introduced was sufficient to cover the coal in eachcase. The kettles were maintained in the open condition and wereuninsulated. Following the period designated for comminution, the excessliquid was poured off, and the coal was allowed to stand in air to dry.There was no mechanical agitation at any time.

The results of chemical comminution by means of moist ammonia for variedexposure times are shown for each coal in Table 4. The extent ofcomminution is indicated by comparison of the material retained on eachsieve before and after comminution. It is clear that staticfragmentation is achieved with both of these coals although the extentof comminution is variable. Under the conditions of these experiments,an apparent steady state with respect to the extent of chemicalcomminution is reached with the Illinois No. 6 coal after 15 minutes.The Pittsburgh Seam coal requires longer exposure under staticconditions with effective breakage after minutes in moist ammonia. Themoisture content of the ammonia prior to addition to the coal was about1 percent. It is thought that the lower rate of reaction of the ammoniawith the Illinois coal is due to the greater moisture content of thiscoal. The following Tables show the results achieved:

TABLE I SOURCE: PITTSBURGH SEAM, DISTRICT 3, MARION COUNTY, WESTVIRGINIA Weight Percent (W/O) Retained TYLER SIEVE +5 5X9 9X12 12 3232X60 60XI00 100X0 TREATMENT:

RAW-NO 61.15 13.74 5.38 9.59 3.99 2.06 4.09 COMMINUTION:

TREATMENT:

LIQUID AMMONIA:

5 MINUTES 53.30 16.70 6.40 11.60 4.90 2.40 4.70 10 MINUTES 49.20 17.007.10 13.50 5.60 2.70 4.90 15 MINUTES 39.50 21.30 8.40 16.50 6.50 2.705.10 60 MINUTES 26.28 20.31 11.91 24.35 8.66 3.21 5.28

TABLE 11 SOURCE: ILLINOIS NUMBER 6 SEAM, DISTRICT 10, MONTGOMERY COUNTYILLINOIS Weight Percent (W/O) Retained TYLER SIEVE +5 5X9 9X12 12 32 3260 60XI00 100 0 TREATMENT:

RAW-NO 59.40 13.30 5.10 10.50 5.00 2.50 4.20 COMMINUTION:

TREATMENT:

MOIST LIQUID AMMONIA 2 MINUTES 23.10 15.60 14.80 25.40 8.50 3.50 8.10 5MINUTES 24.60 15.40 14.60 26.40 8.20 3.60 14.20 15 MINUTES 15.40 19.9016.40 27.40 8.70 3.90 $4 '10 30 MINUTES 15.70 10.50 15.40 26 9.10 4 '1017.0

Tests with other bituminous coal samples have given with, in general,increasing times for coals selected from seams located progressively tothe East. For example Iowa Lower Cherokee presents one extreme withsubstantial size reductions, similar to those shown for Illinois Number6 blocks several inches in each dimension after less than two minutesexposure to moist liquid ammonia. Pittsburgh Seam Coals are the mostdifficult bituminous coals to comminute with maximum exposure times ofone hour needed to effect the necessary size reduction.

Tests were carried out to establish that the comminution effect couldnot be attributed to the low temperature of the moist liquid ammonia. Inthese tests, samples of Illinois Number 6 and Pittsburgh coals wereimmersed in tap water at room temperature for one hour,

Cherokee Coal, the most sensitive coal to the comminuting effects ofmoist liquid ammonia, was chilled by immersion in a liquid-gas stream ofnitrogen for approximately 5 minutes and thawed in air. Microscopicexamination indicated that coal breakage had not been 1 effected by thefreezing process. It can therefore be concluded that it is the chemicaleffect of the moist ammonia which has caused weakening or fracture ofthe interfacial bonds and not the freezing and thawing: However,expansion of the ammonia from the liquid phase to the vapor phase have arole in the process.

Float-sink tests in 1.62 specific gravity tetrachloroethylene wereconducted to determine the relative amounts of coal and rock and mineralmatter for raw and chemically comminuted samples in each sieve rangethrough 100 mesh. The 100 X 0 fraction was deleted due to the attendantdifficulties in handling.

FIG. 2 shows graphically the size distribution of raw and comminutedPittsburgh coal. The large decrease in the +5 fraction and the smallincrease in the 60 X 100 fraction are particularly significant. FIG. 3shows the size distribution of that portion of the raw and comminutedcoal having a specific gravity less than 1.62, in

other words, the organic portion of the coal. Comparison of the valuesfor the various fraction of the untreated coal with and withoutseparation by flotation shows little difference between them.'Thisresult implies that the inorganic material is suspended in enoughorganic material so that the particles float. However, comparison of the+5 fractions of the untreated and treated coal shows that the treatedcoal fraction is sub- I stantially smaller. Consequently, it can beinferred that treatment has separated a large portion of the inorganicmatter from the organic matrix, allowing the inorganic matter to sink.

FIGS. 4 and 5 give the results of similar tests on Illinois No. 6 seamcoaLHere the reduction in the float portion of the +5 fraction bytreatment with moist ammonia is even more striking. Also, as can be seenfrom FIG. 4, the degree of fragmentation by treatment with moist ammoniais greater than with the Pittsburgh seam coal.

The quantity of coal in the size range 9 X 32 after comminution at theexpense of the plus 9 mesh coal -with the build-up of relatively fewvery fine particles is 'characteristic of fragmentation by moistammonia. The absence of plus 5 floating material and minus floatingmaterial in the case of Illinois Number 6 is espe cially indicative ofthe ability of the comminution effect to reduce the size of large pieceswith little increase in the range minus 60 mesh. Further, for most ofthe coals tested, approximately percent of the recoverable coal is plus32 mesh. This reduction in the amount of fines to be handled is asignificant economic factor and greatly simplifies handling,transportation and storage of the cleaned coal fuel.

Table III summarizes the data in analyzing the float and sink portionsof each of the sieve fractions of the Illinois Number 6 samples. Thesamples were analyzed -for ash, pyritic sulfur and thermal value.

The data show that the float fraction represents 98 percent of thethermal value of the composite samples with I 66 percent less ash and 71percent less pyritic sulfur than in the original.

Table IV shows results with a similar analysis made from a mechanicallyground sample having a similar size distribution- TABLE III Evaluationof Chemical Comminution For Removing Pyritic Sulfur and Ash FromIllinois No. 6

Seam Coal.

ANALYSIS OF CHEMICALLY COMMINUTED SAMPLE ANALYSIS OF MECHANICALLY GROUNDSAMPLE HAVING SIMILAR SIZE DISTRIBUTION TO THAT OF TABLE III FLOATCHEMICAL ANALYSIS, DRY WEIGHT BASIS REDUCTION 8L SINK ASH PYRITICBTU/LB. ASH PYRITIC WEIGHT SULFUR SULFUR Float at 1.62 75.5 8.29 0.7213,783 66.0 60.9 Sink at 1.62 24.5 73.98 5.31 Composite 100.0 24.41 1.8410,1 10

The results achieved by mechanical grinding are equivalent to those forchemical comminution as far as ash reduction is concerned and somewhatinferior with respect to pyritic sulfur. However, it must be noted thatseparation was carried out by flotation, which is not a productionprocedure. Separation into organic matter and inorganic matter bysieving would have failed completely, by definition.

Despite fluctuations in total pyritic sulfur content among varioussamples tested, the results indicate that the comminution process of thepresent invention consistently yields the lowest overall pyritic sulfurand total sulfur contents. The principal reason, of course, is that thecomminution with moist ammonia does not reduce the size of the inorganicimpurities, so that either sieving or flotation processes can be usedfor separation of the ash and pyrite from the coal itself.

For many coals the organic sulfur content lies between 0.4 and 0.7percent by weight. Other coals such as Pittsburgh Redstone have from 0.7to 1.0 percent of organic sulfur. Since virtually all of the inorganicsulfur is removable by treatment with moist ammonia, it is evident thatthere is a huge quantity of coal which can be treated to bring thesulfur content to 1.0 percent or lower.

As aforenoted, the effect of increasing the moisture content in theammonia is to decrease the rate at which weakening of interfacial bondsand comminution occur. In one test, successive batches of bituminouscoal containing up to 11 percent moisture were treated with recycledammonia. The ratios were 1 pound of ammonia to pounds of coal. Startingwith essentially anhydrous ammonia, the water content after treatingeach successive batch of coal was as follows:

Water content of Ammonia The entries in the above Table are given interms of weight percent of water in the composition.

As aforenoted, the moisture content can range up to about 70 percent ofthe total of the water-ammonia solution. Even concentrated ammoniumhydroxide having an ammonia content of 28-29 percent can be used, butthe reaction rate is low. From the standpoint of the kinetics of thereaction, the preferred maximum concentration of water is 25 percent byweight. When the water content of the solution reaches a level such thatthe kinetics are judged uneconomic, the ammonia can be separated fromthe water by known means and reused. The quantity of ammonia lost in theprocess is small, so that the cost of ammonia does not represent a majorfactor in the economics of the process.

The process has been tested on coals ranging from lignite to anthracite.It has been found effective with all of these types of coal; however,the rate of comminution with anthracite is lower than with the othercoals tested. It appears that the rate of comminution is proportional tothe inorganic impurity content of the coal. For this reason the theprocess is particularly important and valuable where the pyrite contentis high.

Comminution of coal with moist ammonia can be effectively utilized inthe mining of coal where the coal is located either in sub-surfacestrata or surface strata. A boring tool is first used as a means ofreaching a subsurface coal seam and for providing a passage throughwhich one or more pipes can be inserted into the seam. The pipesessentially seal the passage, and the pipes can be arranged, preferablyessentially concentrically, so that moist liquid ammonia and an inertcarrier gluid can be brought to the seam (not necessarilysimultaneously) and a suspension of comminuted coal can be brought tothe surface where the contaminants can be separated from the suspension.An inert gas flowing at high rate can be used and the comminuted coalcan be fluidized. Alternatively, the moist ammonia can first be injectedor circulated through the coal seam using apparticularly suitable forauger and for strip-mining. The.

ammonia can be recovered by a suitable process for recycling. The coalparticles can then be classified for further size reduction in anammonia atmosphere, for further contaminant isolation or for directsale.

FIG. 1 shows schematically how such a process is carried out. Moistliquid ammonia, stored in tank 1 is supplied to pipe 2 and transportedtherethrough to coal seam 3 lying below the surface of the earth 4. Aninert fluid stored in tank 6 is likewise transported through pipe 2 tocoal seam 3. The rate of supply of inert fluid is such that coalfragments produced by contact of the moist ammonia with the coal seamare suspended or fluidized and carried upward through pipe 7. From pipe7 the product is carried to separator 8 which screens the coal fragmentsfrom rock and other impurity objects which are of larger size. Thefragmented coal is transferred to coal storage bin 9. The ammoniarecovered in separator 8 is transferred back to tank 1. Similarly, whenan inert gas is used for fluidizing the coal fragments, it is returnedto storage tank 6. The various pumps, valves, etc. necessary for theoperation are not shown since the provision of such accessories would bewell within the skill of one familiary with the art. Furthermore,although pipes 2 and 7 are shown as being concentric, this is merely amatter of convenience since the drilling of only one hole is requiredwith such an arrangement. Also three concentric tubes could asconveniently be used, one to carry the moist ammonia, a second to carryinert gas, and a third to lead the fluidized coal fragments to thesurface.

Treatment of coal chunks with liquid ammonia in accordance with thepresent invention is also useful where the chunk coal is producedmechanically as by a borer or auger.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in carrying out the above methodwithout departing from the spirit and scope of the invention, it isintended that all matter contained in the above description shall beinterpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific feaing said coal with an effectiveamount of moist ammonia where the ratio of water to ammonia is up to72:28 by weight.

2. The method as defined in claim 1, where the ratio of water to ammoniais up to :75 by weight.

1. A METHOD OF REDUCING INTERLAYER FORCES AT NATURAL INTERFACES PRESENTIN COAL, COMPRISING THE STEP OF TREATING SAID COAL WITH AN EFFECTIVEAMOUNT MOIST AMMONIA WHERE THE RATIO OF WATER TO AMMONIA IS UP TO 72.28BY WEIGHT.
 1. A method of reducing interlayer forces at naturalinterfaces present in coal, comprising the step of treating said coalwith an effective amount of moist ammonia where the ratio of water toammonia is up to 72:28 by weight.